Observations on the vegetative anatomy of Austrobaileya: habital, organographic and phylogenetic conclusions

For the single species of Austrobaileya (Austrobaileyaceae), quantitative a nd qualitative data are offered on the basis of a mature stem and a root of moderate diameter. Data available hitherto have been based on stems of sma ll to moderate diameter, and roots have not previously been studied. Scanni ng electron microscope (SEM) photographs are utilized for roots, and show c ompound starch grains. Roots lack sclerenchyma but have relatively narrow v essels and abundant ray tissue. Recent phylogenies group Austrobaileyaceae with the woody families Illiciaceae, Schisandraceae, and Trimeniaceae (thes e four may be considered Illiciales), and somewhat less closely with the ve sselless families Amborellaceae and Winteraceae; and the aquatic families C ambombaceae and Nymphaeaceae. The vessel-bearing woody families above share vessels with scalariform perforation plates; bordered bars on plates; pit membrane remnants present in perforations; lateral wall pitting of vessels mostly alternate and opposite; tracheids and/or septate fibre-tracheids pre sent; axial parenchyma vasicentric (sometimes abaxial); rays Heterogeneous Type I; ethereal oil cells present; stomata paracytic or variants of paracy tic. Although comparisons between vessel-bearing and vesselless families mu st depend on fewer features, Amborellaceae and Winteraceae have no features incompatible with their inclusion in an expanded Illiciales. (C) 2001 The Linnean Society of London.